/////////////////////////////////////////////////////////////////////////////////
// Paint.NET                                                                   //
// Copyright (C) dotPDN LLC, Rick Brewster, Tom Jackson, and contributors.     //
// Portions Copyright (C) Microsoft Corporation. All Rights Reserved.          //
// See src/Resources/Files/License.txt for full licensing and attribution      //
// details.                                                                    //
// .                                                                           //
/////////////////////////////////////////////////////////////////////////////////

// Based on: http://msdn.microsoft.com/library/default.asp?url=/library/en-us/dnaspp/html/colorquant.asp

using PaintDotNet;
using System;
using System.Collections;
using System.Collections.Generic;
using System.Drawing;
using System.Drawing.Imaging;

namespace PaintDotNet.Data.Quantize
{
    internal unsafe class OctreeQuantizer 
        : Quantizer
    {
        private bool enableTransparency;
        private Octree octree;
        private int maxColors;

        /// <summary>
        /// Construct the octree quantizer
        /// </summary>
        /// <remarks>
        /// The Octree quantizer is a two pass algorithm. The initial pass sets up the octree,
        /// the second pass quantizes a color based on the nodes in the tree
        /// </remarks>
        /// <param name="maxColors">The maximum number of colors to return</param>
        /// <param name="maxColorBits">The number of significant bits</param>
        /// <param name="enableTransparency">If true, then one color slot in the palette will be reserved for transparency. 
        /// Any color passed through QuantizePixel which does not have an alpha of 255 will use this color slot.
        /// If false, then all colors should have an alpha of 255. Otherwise the results may be unpredictable.</param>
        public OctreeQuantizer(int maxColors, bool enableTransparency) 
            : base(false)
        {
            if (maxColors > 256)
            {
                throw new ArgumentOutOfRangeException("maxColors", maxColors, "The number of colors should be 256 or less");
            }

            if (maxColors < 2)
            {
                throw new ArgumentOutOfRangeException("maxColors", maxColors, "The number of colors must be 2 or more");
            }

            this.octree = new Octree(8); // 8-bits per color
            this.enableTransparency = enableTransparency;
            this.maxColors = maxColors - (this.enableTransparency ? 1 : 0); // subtract 1 if enableTransparency is true
        }

        /// <summary>
        /// Process the pixel in the first pass of the algorithm
        /// </summary>
        /// <param name="pixel">The pixel to quantize</param>
        /// <remarks>
        /// This function need only be overridden if your quantize algorithm needs two passes,
        /// such as an Octree quantizer.
        /// </remarks>
        protected override void InitialQuantizePixel(ColorBgra *pixel)
        {
            this.octree.AddColor(pixel);
        }

        /// <summary>
        /// Override this to process the pixel in the second pass of the algorithm
        /// </summary>
        /// <param name="pixel">The pixel to quantize</param>
        /// <returns>The quantized value</returns>
        protected override byte QuantizePixel(ColorBgra *pixel)
        {
            byte paletteIndex = 0;

            if (!this.enableTransparency || pixel->A == 255)
            {
                paletteIndex = (byte)this.octree.GetPaletteIndex(pixel);
            }
            else
            {
                paletteIndex = (byte)this.maxColors; // maxColors will have a maximum value of 255 is enableTransparency is true
            }

            return paletteIndex;
        }

        /// <summary>
        /// Retrieve the palette for the quantized image
        /// </summary>
        /// <param name="original">Any old palette, this is overwritten</param>
        /// <returns>The new color palette</returns>
        protected override ColorPalette GetPalette(ColorPalette original)
        {
            // First off convert the octree to _maxColors colors
            List<Color> palette = this.octree.Palletize(maxColors);

            // Then convert the palette based on those colors
            for (int index = 0; index < palette.Count; index++)
            {
                original.Entries[index] = palette[index];
            }

            // Fill the rest of the palette with transparent
            for (int i = palette.Count; i < original.Entries.Length; ++i)
            {
                original.Entries[i] = Color.FromArgb(255, 0, 0, 0);
            }

            // Add the transparent color
            if (this.enableTransparency)
            {
                original.Entries[this.maxColors] = Color.FromArgb(0, 0, 0, 0);
            }

            return original;
        }

        /// <summary>
        /// Class which does the actual quantization
        /// </summary>
        private class Octree
        {
            /// <summary>
            /// Construct the octree
            /// </summary>
            /// <param name="maxColorBits">The maximum number of significant bits in the image</param>
            public Octree(int maxColorBits)
            {
                _maxColorBits = maxColorBits;
                _leafCount = 0;
                _reducibleNodes = new OctreeNode[9];
                _root = new OctreeNode(0, _maxColorBits, this); 
                _previousColor = 0;
                _previousNode = null;
            }

            /// <summary>
            /// Add a given color value to the octree
            /// </summary>
            /// <param name="pixel"></param>
            public void AddColor(ColorBgra *pixel)
            {
                // Check if this request is for the same color as the last
                if (_previousColor == pixel->Bgra)
                {
                    // If so, check if I have a previous node setup. This will only ocurr if the first color in the image
                    // happens to be black, with an alpha component of zero.
                    if (null == _previousNode)
                    {
                        _previousColor = pixel->Bgra;
                        _root.AddColor(pixel, _maxColorBits, 0, this);
                    }
                    else
                    {
                        // Just update the previous node
                        _previousNode.Increment(pixel);
                    }
                }
                else
                {
                    _previousColor = pixel->Bgra;
                    _root.AddColor(pixel, _maxColorBits, 0, this);
                }
            }

            /// <summary>
            /// Reduce the depth of the tree
            /// </summary>
            public void Reduce()
            {
                int index;

                // Find the deepest level containing at least one reducible node
                for (index = _maxColorBits - 1; 
                     (index > 0) && (null == _reducibleNodes[index]); 
                     index--)
                {
                    // intentionally blank
                }

                // Reduce the node most recently added to the list at level 'index'
                OctreeNode node = _reducibleNodes[index];
                _reducibleNodes[index] = node.NextReducible;

                // Decrement the leaf count after reducing the node
                _leafCount -= node.Reduce();

                // And just in case I've reduced the last color to be added, and the next color to
                // be added is the same, invalidate the previousNode...
                _previousNode = null;
            }

            /// <summary>
            /// Get/Set the number of leaves in the tree
            /// </summary>
            public int Leaves
            {
                get 
                { 
                    return _leafCount; 
                }

                set 
                { 
                    _leafCount = value; 
                }
            }

            /// <summary>
            /// Return the array of reducible nodes
            /// </summary>
            protected OctreeNode[] ReducibleNodes
            {
                get 
                { 
                    return _reducibleNodes; 
                }
            }

            /// <summary>
            /// Keep track of the previous node that was quantized
            /// </summary>
            /// <param name="node">The node last quantized</param>
            protected void TrackPrevious(OctreeNode node)
            {
                _previousNode = node;
            }

            private Color[] _palette;
            private PaletteTable paletteTable;

            /// <summary>
            /// Convert the nodes in the octree to a palette with a maximum of colorCount colors
            /// </summary>
            /// <param name="colorCount">The maximum number of colors</param>
            /// <returns>A list with the palettized colors</returns>
            public List<Color> Palletize(int colorCount)
            {
                while (Leaves > colorCount)
                {
                    Reduce();
                }

                // Now palettize the nodes
                List<Color> palette = new List<Color>(Leaves);
                int paletteIndex = 0;

                _root.ConstructPalette(palette, ref paletteIndex);

                // And return the palette
                this._palette = palette.ToArray();
                this.paletteTable = null;
                
                return palette;
            }

            /// <summary>
            /// Get the palette index for the passed color
            /// </summary>
            /// <param name="pixel"></param>
            /// <returns></returns>
            public int GetPaletteIndex(ColorBgra *pixel)
            {
                int ret = -1;
                
                ret = _root.GetPaletteIndex(pixel, 0);

                if (ret < 0)
                {
                    if (this.paletteTable == null)
                    {
                        this.paletteTable = new PaletteTable(this._palette);
                    }

                    ret = this.paletteTable.FindClosestPaletteIndex(pixel->ToColor());
                }

                return ret;
            }

            /// <summary>
            /// Mask used when getting the appropriate pixels for a given node
            /// </summary>
            private static int[] mask = new int[8] { 0x80, 0x40, 0x20, 0x10, 0x08, 0x04, 0x02, 0x01 };

            /// <summary>
            /// The root of the octree
            /// </summary>
            private OctreeNode _root;

            /// <summary>
            /// Number of leaves in the tree
            /// </summary>
            private int _leafCount;

            /// <summary>
            /// Array of reducible nodes
            /// </summary>
            private OctreeNode[] _reducibleNodes;

            /// <summary>
            /// Maximum number of significant bits in the image
            /// </summary>
            private int _maxColorBits;

            /// <summary>
            /// Store the last node quantized
            /// </summary>
            private OctreeNode _previousNode;

            /// <summary>
            /// Cache the previous color quantized
            /// </summary>
            private uint _previousColor;

            /// <summary>
            /// Class which encapsulates each node in the tree
            /// </summary>
            protected class OctreeNode
            {
                /// <summary>
                /// Construct the node
                /// </summary>
                /// <param name="level">The level in the tree = 0 - 7</param>
                /// <param name="colorBits">The number of significant color bits in the image</param>
                /// <param name="octree">The tree to which this node belongs</param>
                public OctreeNode(int level, int colorBits, Octree octree)
                {
                    // Construct the new node
                    _leaf = (level == colorBits);

                    _red = 0;
                    _green = 0;
                    _blue = 0;
                    _pixelCount = 0;

                    // If a leaf, increment the leaf count
                    if (_leaf)
                    {
                        octree.Leaves++;
                        _nextReducible = null;
                        _children = null; 
                    }
                    else
                    {
                        // Otherwise add this to the reducible nodes
                        _nextReducible = octree.ReducibleNodes[level];
                        octree.ReducibleNodes[level] = this;
                        _children = new OctreeNode[8];
                    }
                }

                /// <summary>
                /// Add a color into the tree
                /// </summary>
                /// <param name="pixel">The color</param>
                /// <param name="colorBits">The number of significant color bits</param>
                /// <param name="level">The level in the tree</param>
                /// <param name="octree">The tree to which this node belongs</param>
                public void AddColor(ColorBgra *pixel, int colorBits, int level, Octree octree)
                {
                    // Update the color information if this is a leaf
                    if (_leaf)
                    {
                        Increment(pixel);

                        // Setup the previous node
                        octree.TrackPrevious(this);
                    }
                    else
                    {
                        // Go to the next level down in the tree
                        int shift = 7 - level;
                        int index = ((pixel->R & mask[level]) >> (shift - 2)) |
                                    ((pixel->G & mask[level]) >> (shift - 1)) |
                                    ((pixel->B & mask[level]) >> (shift));

                        OctreeNode child = _children[index];

                        if (null == child)
                        {
                            // Create a new child node & store in the array
                            child = new OctreeNode(level + 1, colorBits, octree); 
                            _children[index] = child;
                        }

                        // Add the color to the child node
                        child.AddColor(pixel, colorBits, level + 1, octree);
                    }

                }

                /// <summary>
                /// Get/Set the next reducible node
                /// </summary>
                public OctreeNode NextReducible
                {
                    get 
                    { 
                        return _nextReducible; 
                    }

                    set 
                    { 
                        _nextReducible = value; 
                    }
                }

                /// <summary>
                /// Return the child nodes
                /// </summary>
                public OctreeNode[] Children
                {
                    get 
                    { 
                        return _children; 
                    }
                }

                /// <summary>
                /// Reduce this node by removing all of its children
                /// </summary>
                /// <returns>The number of leaves removed</returns>
                public int Reduce()
                {
                    int children = 0;
                    _red = 0;
                    _green = 0;
                    _blue = 0;

                    // Loop through all children and add their information to this node
                    for (int index = 0; index < 8; index++)
                    {
                        if (null != _children[index])
                        {
                            _red += _children[index]._red;
                            _green += _children[index]._green;
                            _blue += _children[index]._blue;
                            _pixelCount += _children[index]._pixelCount;
                            ++children;
                            _children[index] = null;
                        }
                    }

                    // Now change this to a leaf node
                    _leaf = true;

                    // Return the number of nodes to decrement the leaf count by
                    return(children - 1);
                }

                /// <summary>
                /// Traverse the tree, building up the color palette
                /// </summary>
                /// <param name="palette">The palette</param>
                /// <param name="paletteIndex">The current palette index</param>
                public void ConstructPalette(List<Color> palette, ref int paletteIndex)
                {
                    if (_leaf)
                    {
                        // Consume the next palette index
                        _paletteIndex = paletteIndex++;

                        // And set the color of the palette entry
                        int r = _red / _pixelCount;
                        int g = _green / _pixelCount;
                        int b = _blue / _pixelCount;

                        palette.Add(Color.FromArgb(r, g, b));
                    }
                    else
                    {
                        // Loop through children looking for leaves
                        for (int index = 0; index < 8; index++)
                        {
                            if (null != _children[index])
                            {
                                _children[index].ConstructPalette(palette, ref paletteIndex);
                            }
                        }
                    }
                }

                /// <summary>
                /// Return the palette index for the passed color
                /// </summary>
                public int GetPaletteIndex(ColorBgra *pixel, int level)
                {
                    int paletteIndex = _paletteIndex;

                    if (!_leaf)
                    {
                        int shift = 7 - level;
                        int index = ((pixel->R & mask[level]) >> (shift - 2)) |
                                    ((pixel->G & mask[level]) >> (shift - 1)) |
                                    ((pixel->B & mask[level]) >> (shift));

                        if (null != _children[index])
                        {
                            paletteIndex = _children[index].GetPaletteIndex(pixel, level + 1);
                        }
                        else
                        {
                            paletteIndex = -1;
                        }
                    }

                    return paletteIndex;
                }

                /// <summary>
                /// Increment the pixel count and add to the color information
                /// </summary>
                public void Increment(ColorBgra *pixel)
                {
                    ++_pixelCount;
                    _red += pixel->R;
                    _green += pixel->G;
                    _blue += pixel->B;
                }

                /// <summary>
                /// Flag indicating that this is a leaf node
                /// </summary>
                private bool _leaf;

                /// <summary>
                /// Number of pixels in this node
                /// </summary>
                private int _pixelCount;

                /// <summary>
                /// Red component
                /// </summary>
                private int _red;

                /// <summary>
                /// Green Component
                /// </summary>
                private int _green;

                /// <summary>
                /// Blue component
                /// </summary>
                private int _blue;

                /// <summary>
                /// Pointers to any child nodes
                /// </summary>
                private OctreeNode[] _children;

                /// <summary>
                /// Pointer to next reducible node
                /// </summary>
                private OctreeNode _nextReducible;

                /// <summary>
                /// The index of this node in the palette
                /// </summary>
                private int _paletteIndex;
            }
        }
    }
}
